Hammer with dampening means for high speed printer



0, 1965 E. A. BROWN ETAL 3,199,550

HAMMER WITH DAMPENING MEANS FOR HIGH SPEED PRINTER Filed Aug. 2. 1961 2Sheets-Sheet 1 q- LO A I!) g k\\ 13:

2 EDGAR A. BROWN A GUNTER H. SCHACHL :(JOGSLQ FIGJ ATTORNEY 1965 E. A.BROWN ETAL 3,199,650

HAMMER WITH DAMPENING MEANS FOR HIGH SPEED PRINTER Filed Aug. 2, 1961 2Sheets-Sheet 2 C5 5 fi i) E? United States Patent HAMMER WITH DAMPENINGMEANS FOR HZGH SPEED PRINTER Edgar A. Brown, Gilroy, and Gunter H.Schacht, San

Jose, Calif., assignors to International Business Machines Corporation,New York, N .Y., a corporation of New York Filed Aug. 2, 1961, Ser. No.128,871 @laims. (61. 197-18) This invention relates generally to highspeed printing devices and in particular to those printers in whichprinting is accomplished on the fly without stopping the movement of thetype relative to the paper.

While serial printers are attractive as output devices for low speedapplications because of their relatively inexpensive manufacture, therelatively low speed of operation of these devices has prevented theirwidespread adoption in many potential uses. The on the fly printer,proposed as one approach to the low cost serial printer problem, has alimitation in speed due to the requirement that the firing pin mustarrive at the type with a high degree of accuracy and the componentsmust recover after a character has been printed. The achievable timeaccuracy with which the firing pin arrives at the type and the recoverytime of the rest of the components after impact limit the speed of theon the fly printer. To illustrate the problem with respect to the timeaccuracy, assuming a character velocity of 300 inches per second, themaximum tolerable variation in time for the print hammer after a printcommand is il6 microseconds. This accuracy is essential if properregistration of the printed image is to be achieved. Print quality maybe affected by the tendency of the firing pin to strike the paper morethan once due to the oscillations induced, and, at high speeds, theseoscillations, if allowed to continue undamped, will affect the nextprint operations since either the impact or the proper timing of thehammer may not be realized.

Previous devices have allowed a long delay between print operations toallow the firing pin oscillations to deteriorate to the point where theymight be ignored. Such devices usually require 20 milliseconds or moredelay between print operations. In a device of this invention, thefiring pin comes to rest within 4 to 6 milliseconds after hammer impactwhich allows a considerable increase in the print speed.

It is therefore an object of our invention to provide an improved highspeed serial printing device.

Another object of our invention is to provide a high speed printer inwhich the print hammer is essentially critically damped.

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescription of a preferred embodiment of the invention as illustrated inthe accompanying drawings.

In the drawings:

FIG. 1 is a diagrammatic illustration of a serial printing device of theinvention.

FIGS. 2a through 2 are schematic representations of the print mechanismat the various points in the print cycle.

The printer shown in FIG. 1 consists generally of a hammer 1 whichimpels a firing pin 2 against tape 3 to transfer the image of a selectedone of the characters of type font 4 located on the periphery of typewheel 5. The firing pin 2 is operated at high speed in response to asignal indicating that the appropriate character is in a position to beprinted. In between the print operations an incremental feed mechanism 6steps the tape into position for the next character to be printed.

The type wheel 5 aflixed to shaft 7 has a type font 4 1 pin 2. A supportbracket 23 contains a threaded aparture,

3,199,659 Patented Aug. 10, 1 965 arranged about the periphery of wheel5. Shaft 7 is driven from any suitable power source (not shown). Shaft 8is driven at an integral multiple of the speed of shaft 7 by appropriategears or belts (not shown). Ball bearing 9 affixed to shaft 8 slightlyoff-center comprises cam 10.

Inking roller 11 mounted on shaft 12 bears against type wheel 5 in amanner to continually replenish the supply of ink on the characters oftype font 4. The roller may be of any suitable type for conveying ink tothe type wheel. In the preferred embodiment this roller has an internalreservoir and a porous wall for conveying the ink from the reservoir tothe type wheel. Power for rotation of inking roller 11 is suppliedthrough the frictional engagement of the roller with the type wheel.

A character image is transferred from type wheel 5 to a printing mediumwhich may be a paper tape 3, as shown in FIG. 2, by means of a firingpin 2. When suitably impelled toward type wheel 5, firing pin 2depresses paper tape 3 against the character located thereunder at thetime of contact to transfer the ink from the character to the tape 3. Apair of flat springs 13 and 14 are afiixed to firing pin 2 and to block15 by appropriate mounting means. A stop 16 is also afiixed to mountingblock 15 to limit the travel of firing pin 2 away from type font 4.Hammer 1. provides means for impelling firing pin 2 toward type font 4.Shaft 17 provides means for pivotally mounting hammer 1. Collars 18 and19 retain'hammer 1 for pivotal movement on shaft 17. Compression spring2%, wound about guide 21 and slidably mounted Within guide 22, biaseshammer 1 in the direction of firing through which guide 22 is passed.Support bracket 23 is afiixed to the base plate by means of screws 24.Threaded guide 22 may be adjusted within support bracket 23 to vary theforce applied to hammer 1 by spring 21. Hammer 1 is retained in theready position by means of electromagnet 25 having a core 26 and aWinding 27. Screws 23 hold electromagnet 25 to the base plate. Whenenergized, winding 27 created sufiicient magnetic flux at pole face 29and 3% to retain hammer l in engagement therewith against the force ofcompression spring 24).

When Winding 27 is momentarily deenergized, ham

mer 1 is free to move under the force of spring and rotates about shaft17, allowing face 31 to strike firing pin 2 and impel it toward typefont 4. Firing .pin 2 contains sufiicient kinetic energy to deflect thetape 3 downward against the moving type font and transfer the ink on theparticular character in position at that time to the lower surface oftape 3. Stop 32 affixed to the base plate by means of screw 33 limitsthe travel of hammer 1. Thus, after a print operation, firing pin 2returns to a position abutting hammer 1 which is at rest against stop todeenergization, a current pulse of opposite polarity could be applied tothe winding 27. Power may then be restored to the winding withoutaffecting subsequent op eration of the hammer l and firing pin 2. Afterthe impression of the character has been transferred to the printingmedium and power has been restored to winding 27, hammer 1 will stillremain against stop 32 since the strength at pole faces 29 and Si) isnot suflicient to attract hammer 1 against the action of spring 20.Electromagnet 27 is used as a latch and therefore does not requiresufiicient magnetic field strength to attract hammer 1 out onlysufiicient field strength to retain hammer 1 in engagement with polefaces 29 and 39 against the force of spring 26. The magnet can be madesubstantially smaller than would be required if it operated to restorehammer 1. The use of an electromagnet in this manner reduces the powerdissipation by a large factor.

Mechanical restoration of hammer 1 to the ready position is accomplishedby means of restore arm 34 which is pivotally mounted on shaft 35 andretained thereon by means of collars 36 and 37. Restore arm 34 is onelever of a bell crank having a second lever 38. A compression spring 39wound about guide 40 which is retained within guide 41 biases lever 34against the ball bearing 9. Mounting bracket 42 has a threaded aperturetherein for guide 41 is afiixed to be base plate by means of screws 43.

Restore arm 34 is retained in the idle position by means ofelectromagnet 44 having a winding 45 and which is mounted against thebase plate by means of screws 46. Energization of Winding 45 providessufiicient magnetic flux at pole faces 47 and 48 to retain restore arm34 against the pole faces in the idle position. With restore arm 34 inthe idle position, it rides out of contact with cam 10. When the highpoint of cam 1 is adjacent the restore arm 34, electromagnet winding 45may be deenergized, thereby allowing the restore arm 34 to be movedupward by the action of spring 39 against lever 38 of the bell crank.Release of restore arm 34 from electromagnet 44 is accomplished by meansof timing circuitry associated with type wheel 5. By releasing therestore arm 34 only when the high point of cam is adjacent the restorearm, a much smoother, predictable motion is achieved.

As the restore arm is moved from the idle to the restore position, ashoulder 49 engages a corresponding portion 50 of hammer 1 and moveshammer 1 from a position abutting stop 32 to a position adjacent polefaces 29 and 313. Since winding 27 is now energized, hammer 1 isretained in engagement with electromagnet 25. Restoration of hammer 1compresses spring 20, and hammer 1 is once again prepared for a printoperation.

Lever 38 of the bell crank has a foot 51 and pawl 52 arrangement at theextremity thereof. A spring 53 biases pawl 52 against foot 51 in amanner to retain the printing medium 3 against the foot during motionaway from the print position. It can be seen that pawl 52 is mountedslightly off-center and therefore exerts a clamping action against tape3 as it moves away from the print position. The foot and pawl oscillatesin a direction away from the print position and toward the printposition. During this latter portion of the cycle, pawl 52 glides freelyalong tape 3. The tape is thus released and the pawl 52 assumes a normalposition without a corresponding movement on the part of the tape. Thisportion of the operation is enhanced by means of a second pawl 54 andspring 55 cooperating with guide pin 56 to prevent reverse movement ofthe tape 3. Also it is apparent that the desired releasing and dampingaction is ensured at high speed by its own inertia. Pawl 54 is pivotallymounted to the base plate and does not move with foot 51 and pawl 52.Movement of the tape away from the print position is not prevented bypawl 54 since this provides an unclamping action between the pawl 54 andguide pin 56. However, return motion is prevented since pawl 54 exerts aclamping action against guide pin 56 to prevent motion of tape 3 in thedirection of the print position.

The rapid stepping motion of the foot 51 and pawl 52 for feeding thetape 3 through the print position is ideal for moving the paper betweenprint operations since it achieves this result during the time hammer 1is being restored. However, this rapid incremental movement of the tape3 is incompatible with the high inertia of the tape feed roll 57 andrequires means for smoothing out this incremental motion so that thetape will not be broken.

While it is possible to drive the feed roll 57 in synchronism with thefeed foot 51 and pawl 52, this represents an unsatisfactory solution dueto the high inertia of the done.

ieaeso roll 57 and the changing diameter which alters the feedrequirements. Similarly, a continuously operating capstan drive isunacceptable since there are occasions when it is esired to hold up thefeed of tape, for example, during a period of time when no printing isbeing done. The continuous feed would result in a blocking or cloggingof the print position during the time when no printing is being Thus,some satisfactory means is necessary to smooth out the incremental feedfrom the foot and pawl to a relatively smooth feed from the storageroll.

To smooth the incremental tape motion to a smooth feed a capstan 58 ismounted on a continuously rotating shaft 59. The tape medium 3 passingfrom storage roll 57 to the print position is deflected about capstan 58by means of guide pins 6%, 61, and 62. A spring 63, aflixed to the baseplate by means of screws, deflects the tape medium between guide pins 69and 61. The deflection of spring 63 depends upon the tension in the tape3 which is in turn a function of the feed requirements from storage roll57. When the storage roll has not supplied sufficient tape to the printposition, the tension increases and the deflection of spring 63 islikewise increased. Spring 63 may be positioned between pin 2 andcapstan 58 to deflect the tape in that region to provide the samefunction. The increased tension in the print medium results in anincrease of the normal force of the tape medium against the capstan.Since the capstan 58 is continuously rotating, the increased normalforce in conjunction with the angular wrap and the coefiicient offriction results in a feed operation from the storage roll 57 by meansof the capstan 58. Thus, the relatively jerky movement caused by theincremental feed of the foot 51 and pawl 52 is converted into a smoothfeed operation and breakage of the tape medium is avoided. If no printcycle takes place, the decreased tension on the tape medium permits anair bearing to exist between tape and capstan. This assures undamagedtape if the printer idles any length of time.

FIGS. 2a2f represent a step-by-step description of the coaction betweenhammer it, firing pin 2, and restore arm In FIG. 2a hammer 1 is in theready position, firing pin 2 is at the rest position, and restore arm 34is in the idle position. All electromagnets are energized to retain theelements at this point. The print operation is initiated by deenergizingthe winding on electromagnet 25, allowing hammer i to move into theposition shown by FIG. 2b. The hammer 1 is now in the strike positionand the firing pin 2 has not yet moved from the rest position. In FIG.2c the hammer 1 has continued its motion to impel firing pin 2 againstprint wheel 5 by the energy contained in the hammer. In FIG. 2d thefiring in has returned to the rest position after the print operationand has been damped by means to be described later. The restore arm 34has been released from electromagnet 44 by deenergization of the windingassociated therewith, and restore arm 34 is following earn it). Thisresults in hammer 1 being moved back into engagement with electromagnet25, now energized to retain hammer 1 against the pole faces thereof.

In FIG. 2e hammer 1 has been completely restored into engagement withelectromagnet Z5, and is retained there. The restore arm 34 is in thecomplete restore position. This is the low point of cam 10. As cam It)continues to rotate, it approaches a position shown in FIG. 2] in whichthe restore arm 34 is again placed into engagement with electromagnet44, now energized to retain the restore arm in the idle position. Thus,the condition shown in FIG. 2a again exists with the hammer 1 in theready position, firing pin 2 in the rest position, and restore arm 34 inthe idle position.

A substantial increase in speed is possible by proper damping of thefiring pin. Without an additional damping arrangement it is necessary towait for the oscillations to damp themselves out before initiatinganother print operation. If this is not done, there is always thepossibility that the hammer may strike the firing pin as the 5 firingpin is oscillating in a direction toward the hammer. This would resultin a slower movement of the firing pin from the ready to the strikeposition and would produce type which is improperly spaced and not asdark as would normally occur. The exploded view of firing pin 2, asshown in FIG. 1, illustrates the additional means which providesessentially critical damping. A chamber 64 within firing pin 2 is sealedand contains a piston 65. Piston 65 has an aperture 66 extending fromend 67 to end 68, permitting air to travel through the piston from oneend of the chamber to the other. A spring 69 biases the piston to oneend of the sealed chamber. It can be seen that the damping means hasabsolutely no effect on the travel of the firing pin as it is initiallystruck by hammer 1, since the piston is spring urged toward the end ofthe firing pin adjacent the hammer. However, when the pin strikes thetype wheel, the piston 65 moves downward against the action of thespring and reduces the rebound velocity of firing pin 2 from the typewheel.

In addition to compressing spring 69, the motion of piston H 65 iseffective to increase the air pressure in the side of the chamber towardwhich it is moving. The aperture 66 through piston 65'allows thecompressed air in one end of the cylinder to pass to the other lowerpressure end. The energy expended in this transfer of air is dissipatedas heat. The size of this aperture is a function of the masses involved,velocities and the spring 69, and will therefore vary from case to caseand with the damping desired. Movement of the piston within the sealedchamber downwardly compresses the spring 69 and causes air to bedisplaced from the end of the chamber including the spring to the end ofthe chamber above the moved piston. As the firing pin returns to itsprevious position, the spring acts upon the piston to compress the airin the upper chamber. of the cylinder and the spring between the pistonand the lower end of the cylinder balance each other out and serve toessentially critically damp the motion of the firing pin, quicklyarresting its oscillations. The aperture within the cylinder is of asize sufiicient to assure high velocity airflow for energy dissipationand is relatedto the mass of the cylinder and the firing pin, togetherwith the physical constants of spring, and the velocities of the variouscomponents to provide the desired damping. It is entirely possible thatthe aperture could be placed as a groove along the outside of the pistonor merely by making the piston of sufficiently smaller diameter than theinside diameter of the chamber.

In the embodiment shown and described, cam 10 rotates at four times thespeed of rotation of the type wheel. Thus, it is possible to print twocharacters for each revolution of the Wheel. For example, a characterwould be printed in the first quadrant, the hammer restored and tapestepped during the passage of the second quadrant, another characterprinted in the third quadrant, and the hammer restored in the fourthquadrant. Since this may be a fairly high speed, conventional camfollowers which increase the moment of inertia of the oscillating arm orhave poor wear characten's-tics have been found to be unsatisfactory.The use of an eccentrically mounted ball bearing 9 in place of theconventional cam has been found to substantially increase the life ofcam follower 34 without any sacrifice in performance of the device. Inoperation the outer rim of cam 10 does not rotate but remainspractically stationary when the follower is bearing against it. Thus,there is no wear on the follower portion of restore arm 34 or the outersurface of the cam even at the high speeds involved.

While the invention has been particularly shown and described withreference to a preferred embodiment thereof, it will be understood bythose skilled in the art that various changes in the form and detailsmay be made therein without departing from the spirit and scope of theinvention.

The compressed air in the upper end What is claimed is:

1. In an on the fly printer having a rotating type font and a firing pinfor coaction therewith to create an impression thereof on a printmedium, hammer means for operating said firing pin, spring actuatormeans for moving said hammer from a ready position to a strike positionto operate said firing pin, first magnetic latch means, means forenergizing said latch means to retain said hammer in the ready positionagainst the force of said spring actuator, pivot means supporting saidhammer for movement by said actuator means to operate said firing pinupon deenergization of said latch means, restore means for said hammercomprising a cam, means for continuously driving said cam at an integralmultiple of the speed of said print wheel, a cam follower operablebetween an idle and a restore position, second magnetic latch means,means for energizing said second latch means to hold said follower inthe idle position, means for deenergizing said second latch means torelease said follower at selected points during rotation of said typefont to follow said cam, and means affixed to said follower for engagingsaid hammer during movement from the idle to the restore position tomove said hammer into said ready position against said first latchmeans.

2. In an on the fly printer having a rotating type font and a firing pinfor coaction therewith to create an impression thereof on a printmedium, hammer means for operating said firing pin, spring actuatormeans for moving said hammer from a ready position to a strike positionto operate said firing pin, first magnetic latch means, means forenergizing said latch means to retain said hammer in the ready positionagainst the force of said spring actuator, pivot means supporting saidhammer for movement by said actuator means to operate said firing pinupon deenergization of said latch means, restore means for said hammercomprising a cam, means for continuously driving said cam, a camfollower operable between an idle and a restore position, secondmagnetic latch means, means for energizing said second latch means tohold said follower in the idle position, means responsive to theposit-ion of said cam for deenergizing said second latch means torelease said follower at selected points during rotation of said cam,and means afiixed to said follower for engaging said hammer duringmovement from the idle to the restore position to move said hammer intosaid ready position against said first latch means.

3. In an on the fiy printer having a rotating type font and a firing pinfor coaction therewith to create an impression thereof on a printmedium, hammer means for operating said firing pin, spring actuatormeans for moving said hammer from a ready position to a strike positionto operate said firing pin, first magnetic latch means, means forenergizing said latch means to retain said hammer in the ready positionagainst the force of said spring actuator, pivot means supporting saidhammer for movement by said actuator means to operate said firing pinupon deenergization of said latch means, restore means for said hammercomprising a cam, means for continuously driving said cam at a higherspeed than the speed of said print wheel, a cam follower operablebetween an idle and a restore position, second magnetic latch means,means for energizing said second latch means to hold said follower inthe idle position, means responsive to the position of said cam fordeenergizing said second latch means to release said follower atselected points during rotation of said cam, and means affixed to saidfollower for engaging said hammer during movement from the idle to therestore position to move said hammer into said ready position againstsaid first latch means.

4. In an on the fly printer having a rotating type font and a firing pinfor coaction therewith to create an impression thereof, on a printmedium hammer means for operating said firing pin, spring actuator meansfor moving said hammer from a ready position to a strike position tooperate said firing pin, first magnetic latch means, means forenergizing said latch means to retain said hammer in the ready positionagainst the force of said spring actuator, pivot means supporting saidhammer for movement by said actuator means to operate said firing pinupon deenergization of said latch means, cam restore means for saidhammer comprising an eccentrically mounted ball bearing, means forcontinuously driving said cam at an integral multiple of the speed ofsaid print wheel, a cam foll wer operable between an idle and restoreposition, second magnetic latch means, means for energizing said secondlatch means to hold said follower in the idle position, means fordeenergizing said second latch means to release said follower atselected points during rotation of said type font to follow said cam,and means afiixed to said follower for engaging said hammer duringmovement from the idle to the restore position to move said hammer intosaid ready position against said first latch means.

5. In an on the fly printer having a rotating type font and a firing pinfor coaction therewith to create an impression thereof on a printmedium, hammer means for operating said firing pin, damping means forsaid firing pin comprising: a chamber within said firing pin, a. pistonmovable within said chamber, said piston having a length less than thelength of said chamber, an aperture through said piston connecting theends thereof, spring means urging said piston into abutting relationshipwith the end of said chamber adjacent the point of impact of said hammerwhereby said pin moves undamped in a first direction after impact butsubsequent movements are damped by the piston and spring within saidchamber, spring actuator means for moving said hammer from a readyposition to a strike position to operate said firing pin, first magneticlatch means, means for energizing said latch means to retain said hammerin the ready position against the force of said spring actuator, pivotmeans supporting said hammer for movement by said actuator means tooperate said firing pin upon deenergization of said latch means, camrestore means for said hammer comprising an eccentrically mounted ballbearing, means for continuously driving said cam at an integral multipleof the speed of said print wheel, a cam follower operable between anidle and a restore position, second magnetic latch means, means forenergizing said second latch means to hold said follower in the idleposition, means for deenergizing said second latch means to release saidfollower at selected points during rotation of said type font to followsaid cam, and means affiXed to said follower for engaging said hammerduring movement from the idle to the restore position to move saidhammer into said ready position.

References Cited by the Examiner UNITED STATES PATENTS 1,542,129 6/25Hayes 226-160 2,323,388 7/43 Fitch et al. 19749 2,328,636 9/43 Fitch eta1. 19749 2,504,759 4/50 Thompson 197133 2,531,875 11/50 Dodge et a1.197-133 2,592,013 4/52 Curley 14529.2 2,625,100 1/53 Williams et a1.101-93 2,854,100 9/58 Bowser et a1 188103 3,041,964 7/62 Simpson et a1101-93 FOREIGN PATENTS 815,046 7/37 France.

1,163,525 9/58 France.

RGBERT E. PULFREY, Primary Examiner.

F ROBERT A. LEIGHEY, EUGENE R. CAPOZIO,

Examiners.

1. IN AN ON THE FLY PRINTER HAVING A ROTATING TYPE FONT AND A FIRING PINFOR COACTION THEREWITH TO CREATE AN IMPRESSION THEREOF ON A PRINTMEDIUM, HAMMER MEANS FOR OPERATING SAID FIRING PIN, SPRING ACTUATORMEANS FOR MOVING SAID HAMMER FROM A READY POSITION TO A STRIKE POSITIONTO OPERATE SAID FIRING PIN, FIRST MAGNETIC LATCH MEANS, MEANS FORENERGIZING SAID LATCH MEANS TO RETAIN SAID HAMMER IN THE READY POSITIONAGAINST THE FORCE OF SAID SPRING ACTUATOR, PIVOT MEANS SUPPORTING SAIDHAMMER FOR MOVMENT BY SAID ACTUATOR MEANS TO OPERATE SAID FIRING PINUPON DEENERGIZATION OF SAID LATCH MEANS, RESTORE MEANS FOR SAID HAMMERCOMPRISING A CAM, MEANS FOR CONTINUOUSLY DRIVING SAID CAM AT AN INTEGRALMULTIPLE OF THE SPEED OF SAID PRINT WHEEL, A CAM FOLLOWER OPERABLEBETWEEN AN IDLE AND A RESTORE POSITION, SECOND MAGNETIC LATCH MEANS,MEANS FOR ENERGIZING SAID SECOND LATCH MEANS TO HOLD SAID FOLLOWER INTHE IDLE POSITION, MEANS FOR DEENERGIZING SAID SECOND LATCH MEANS TORELEASE SAID FOLLOWER AT SELECTED POINTS DURING ROTATION OF SAID TYPEFONT TO FOLLOW SAID CAM, AND MEANS AFFIXED TO SAID FOLLOWER FOR ENGAGINGSAID HAMMER DURING MOVEMENT FROM THE IDLE TO THE RESTORE POSITION TOMOVE SAID HAMMER INTO SAID READY POSITION AGAINST SAID FIRST LATCHMEANS.